Global excess deaths associated with heatwaves in 2023 and the contribution of human-induced climate change

Abstract: An unprecedented heatwave swept the globe in 2023, marking it one of the hottest years on record and raising concerns about its health impacts. However, a comprehensive assessment of the heatwave-related mortality and its attribution to human-induced climate change remains lacking. We aim to address this gap by analyzing high-resolution climate and mortality data from 2,013 locations across 67 countries/territories using a three-stage modeling approach. First, we estimated historical heatwave-mortality associations using a quasi-Poisson regression model with distributed lag structures, considering lag effects, seasonality, and within-week variations. Second, we pooled the estimates in meta-regression, accounting for spatial heterogeneity and potential changes in heatwave-mortality associations over time. Third, we predicted grid-specific (0.5 0.5) association in 2023 and calculated the heatwave-related excess deaths, death ratio, and death rate per million people. Attribution analysis was conducted by comparing heatwave-related mortality under factual and counterfactual climate scenarios. We estimated 178,486 excess deaths (95% empirical confidence interval [eCI], 159,892≥204,147) related to the 2023 heatwave, accounting for 0.73% of global deaths, corresponding to 23 deaths per million people. The highest mortality rates occurred in Southern (120, 95% eCI, 116≥126), Eastern (107, 95% eCI, 100≥114), and Western Europe (66, 95% eCI, 62≥70), where the excess death ratio was also higher. Notably, 54.29% (95% eCI, 45.71%≥61.36%) of the global heatwave-related deaths were attributable to human-induced climate change. These results underscore the urgent need for adaptive public health interventions and climate mitigation strategies to reduce future mortality burdens in the context of increasing global warming.

Public summary: Over 178,000 global deaths associated with the 2023 heatwave, equivalent to 23 deaths per million. -Southern and Eastern Europe had the highest heatwave-related mortality burden. -Heatwave-related deaths were concentrated in subtropical and temperate zones of the Northern Hemisphere. -More than half (54.29%) of heatwave-related deaths were attributable to human-induced climate change.